Hybrid soap stamping bars

Details Hybrid soap stamping bars Hybrid soap stamping bars

1999-05-27

2001-09-04

Mackey, James P. (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Preform reshaping or resizing means: or vulcanizing means...

Shaping surfaces per se

C249S115000, C264S338000, C425S470000, C427S133000, C427S256000

Reexamination Certificate

active

06283744

ABSTRACT:

The invention relates to stamping dies, and particularly soap stamping dies. By soap in this context is meant a solid product containing soap, synthetic detergent, or a combination thereof which comprises at least 20% of the product.
Soap stamping dies generally consist of a pair of symmetrically opposed die halves, each having a cavity, which are brought together about the substrate to form a stamped billet of substrate. A critical part of the stamping process involves the release of the stamped billet from a die half after separation of the halves. Various methods of facilitating die release have been proposed, including the use of die ejectors, coating the substrate stamping surfaces with talcum powder or a release fluid, or coating the stamping surfaces with an elastomeric coating.
For example, EP 285 722 discloses a composite coating for imparting an abrasion resistant release surface to a substrate, the coating comprising a thermal sprayed metal matrix having a film of silicone impregnated thereon.
The method of coating dies with elastomeric coatings has proven to be a particularly successful means of facilitating die release; however, various problems have been encountered with this method. Firstly, elastomers, when used in stamping machines, are continually exposed to shear strain and deformation, due to the stamping action of the dies. This leads to the elastomeric coatings becoming damaged over relatively short periods of time. When this happens, which in the case of continuously operating stampers can be as often as every three weeks, the coatings on the dies needs to be replaced, which involves shutting down the machines for prolonged periods of time.
A further problem with such coatings is that during application, some elastomers may sag and run down non-horizontal faces of the die before curing, which results in an uneven surface which is non-uniform in thickness. Such faults on the stamping surface of the die generally translate into faults on the stamped product.
A further problem with some elastomers is that they require a bonding agent to achieve suitable adhesion with the die surface, which bonding agents generally comprise reactive chemicals, having high hazard classification and volatile organic compounds as carrier solvents. Modern health, safety and environmental legislation imposes increasingly strict controls on the industrial use of these materials.
It is a desirable object of the invention to provide a substrate stamping surface for stamping dies which overcomes or improves on at least some of the above problems.
In a first aspect of the invention, there is provided a stamping die having a substrate stamping surface which comprises a base matrix of open structure having a coating of elastomeric material applied thereon. In this specification, the term “open structure”, when applied to the matrix, is taken to mean that the surface of the matrix is non-uniform and if viewed, in cross section, would include a multiplicity of depressions, peaks and plateaus. Typically the peak to depression distance might be in the region of 50-200 microns, or 70-150 microns. When applied to such a matrix surface, the elastomer fills the depressions and coats into the matrix in such a way that it becomes strongly bonded to the matrix, by virtue of the interlocking nature of the bonding. Further, low viscosity elastomer compositions, when applied to such open matrix structures, are retained by the matrix until they cure, and thus the elastomers are less likely to drain or sag.
In a preferred embodiment of the invention, the stamping surface is a composite structure with the matrix protruding through the elastomeric coating in places. Ideally, the surface is predominantly elastomer.
Generally, the matrix comprises a ceramic or metal material which, in one embodiment, is applied to the die by means of plasma or flame spraying techniques. Alternatively, the matrix may be formed by means of laser or mechanical micro-machining, chemical etching, anodisation, spark erosion, plasma or ion beam treatment of the material of the die. However, the invention is not restricted to the above methods of forming an open structure matrix.
A full description of the term “elastomer” and specific examples of suitable elastomers can be found in the Applicants published European Patent Application No. 95924225, the content of which is incorporated herein by reference. In a preferred aspect of the invention, the elastomer comprises a silicone or a fluorosilicone elastomer.
Suitable elastomers for use in dies according to the invention typically have a relatively low level of damping, and a low modulus. According to a further aspect preferred elastomers may typically contain carbon, and hence be the “R”, “M” or “U” classes, as classified by the American Society for Testing and Materials D1418. These classes are the unsaturated carbon chain elastomers, saturated carbon chain elastomers, and elastomers containing carbon, nitrogen and oxygen in the polymer chain. Elastomers of this type have been found to be relatively easy to refurbish on dies, for example by burning off entirely the residue of the old elastomer coating.
Suitable carbon containing elastomers include polyurethane, acrylonitrile butadiene rubber, and hydrogenated acrylonitrile butadiene rubber, especially hydrogenated acrylonitrile butadiene rubber. Examples of the latter include Therban (ex. Bayer) and Zetpol (ex. Zeon).
The invention also relates to a process for making a stamping die, the process comprising the steps of:
preparing an open structure matrix surface on the die surface; and
applying a coating of elastomer onto the matrix.
Ideally the process includes the subsequent step of curing the elastomer.
Typically, the matrix forming step includes the matrix forming methods referred to above.
The invention also relates to the use of composite hybrid coatings of the type comprising an open structure base matrix having an elastomeric coating applied thereon as substrate stamping surfaces in stamping dies.
Ideally, the resultant hybrid coating includes pockets of matrix protruding through the elastomeric coating.
The invention also relates to a process for stamping a product, such as for example a detergent bar, by employing a stamping die having a stamping surface comprising a base matrix of open structure having a coating of elastomeric material applied thereon, the process comprising the steps of:
feeding a product composition to the stamping die;
stamping the composition in the die to form a stamped product; and
releasing the stamped product from the die.
Ideally, the product being stamped will be a detergent composition such as for example soap. However the process and device of the invention is similarly envisaged for use in the stamping of various diverse products such as, for example, tablets and foods.
Coatings and substrate stamping surfaces prepared according to the invention give excellent metal-elastomer interfacial bond strength. In many cases, the bond strength obviates the need for the use of separate bonding agents. Hence in a further aspect of the invention there is provided an elastomer coated die which is absent a bonding agent or primer between the metal die and the elastomer layer. Furthermore, the matrix of the invention provides a support surface with multiple points of contact for the elastomer applicator, such that the elastomer may be pushed deep into the matrix, wetting the texture and resulting in excellent mechanical interlocking and elastomer-base adhesion. The coating is of uniform and optimum thickness, controlled by the maximum peak height of the matrix texture.
With coatings of the invention, the functional elastomer coating is protected from accidental damage by the pockets of hard matrix which protrude through the elastomer coating in embodiments where this is the case. Thus, improved resistance to physical damage can be achieved even when relatively soft and fragile elastomers are used. The shear strain that occurs in the elastomer at key places on the die surface is minimised, since zones of

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